The present invention relates to a lance hoist for a basic oxygen steelmaking furnace and, more particularly, is directed to such a hoist wherein a detector is provided to sense the build up of a slag skull on the lance.
The build up of slag skulls on the lances of basic oxygen steelmaking furnaces is a common occurrence. It is troublesome because, if permitted to become excessive, it ultimately restricts passage of the lance through the lance port of the hood used with the furnace. In the prior art, the occurrence of such excessive build up was generally detected either visually, or as a result of impact of the skull against the hood. Prior art hoods typically employed doors on the lance port which could open to permit the passage of a lance skull through the port. Because of the extreme temperatures involved, recent visual detection techniques have employed television cameras. Once detected, the skulls have been removed by removing the lance from the furnace and breaking the skull away.
The problem of lance skull build up has become particularly acute with modern basic oxygen steelmaking furnaces because such furnaces employ extremely expensive hoods for pollution control purposes and the hoods are typically not provided with lance port doors to facilitate the passage of a large skull through the port. Such hoods make visual detection of the skull build up difficult and are likely to incur very costly damage if impacted by a lance skull.
In extreme cases, where lance skulls have impacted against the hoods of furnaces, lances have been totally lost and the lives of operating personnel have been lost. Additionally, when a skull builds up to the point where it impacts the hood of a furnace, the loss of large amounts of furnace operating time inevitably results.
Probably the most significant prior art to the present invention is U.S. Pat. No. 3,708,159. That patent discloses a lance hoist having a load cell and position transmitter incorporated thereinto to detect when the lance contacts the surface of the molten metal in a basic oxygen steelmaking furnace. The patent makes no suggestion, however, of detecting the build up of a lance skull and, apparently, is not concerned with that problem.
U.S. Pat. Nos. 1,507,598 and 4,032,020 are of interest in that they teach the employment of hoisting apparatuses wherein load detectors are employed in the apparatuses. The patents are not, however, concerned with the build up of lance skulls in basic oxygen steelmaking furnaces, or the problems associated with such build up.